Hygienic and Microbial Quality of Yoghurt Mahendra Pal*, Misgana Tefera*, Asmelash Tasew*,Tujuba Jergefa*, Asefa Deressa** *Department of Microbiology, Immunology & Public Health, College of Veterinary Medicine and Agriculture, Addis Ababa University, P.O. Box 34, Debre Zeit, Ethiopia ** Ethiopian Institute of Public Health, P.B.No.1242, Addis Ababa, Ethiopia Email :
[email protected]
ABSTRACT Yoghurt is a versatile food as it is an important source of calcium, phosphorus, magnesium, potassium, riboflavin, vitamin A and protein. As a fermented milk product, it is a natural source of probiotics, which helps to maintain a healthy gut and immune system. The popularity of yoghurt has increased due to its perceived health benefits resulting in significant increase in consumption. Many types of stirred yoghurt are available in the market, varying in fat, sugar, texture, flavor and type of fruits. It has keeping quality of 1-2 days at ambient temperature, and 1 week under refrigerated condition. Microbes in yoghurt may be derived from a variety of sources. The presence of microbes in daily products including yoghurt are undesirable, at these render the milk products of inferior quality. Yeasts and moulds are mainly responsible for the spoilage of yoghurt, as they are not affected by low pH. Microbiological specifications should be applied to some additive employed in the manufacture of yoghurt. Recently, the BioLumix test method has been developed for rapid detection of coliforms, yeasts and moulds. It is emphasized that the activity of starter culture used for the production of yoghurt should be critically monitored periodically to get a product of good quality. Education of food handlers about the importance of high standards of personal hygiene is very essential for hygienic production of milk products in dairy industries. In addition, the application of GHP and HACCP during the production of yoghurt is highly imperative from food safety point of view. Key words: Bacteria, Food safety, Health benefits, Hygiene, Moulds, Probiotics,Yeasts, Yoghurt
INTRODUCTION Milk is used globally in the manufacturing of different types of dairy products. In India, people are very fond of milk made preparations, and hence, a large variety of milk products are available in the market (Pal and Jadhav,2013a). The cheese, butter, yoghurt, and milk power have captured global market. Yoghurt is one of the oldest produced foods in human history. It is a unique food, which is consumed This paper is dedicated in the memory of late Dr. Jacob Nufer, a Swiss Veterinarian, who performed the first successful caesarean section upon a living woman in 1500. Since then, this technique is widely used to deliver babies throughout the world.
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worldwide, without the restriction of any taboo, tradition or religion. Cow milk is most commonly used worldwide to prepare yoghurt. However, the milk from goats, camel, water buffaloes, and yaks are also employed to make yoghurt. The name yoghurt is derived from the Turkish word ‘Jugurt’ reserved for any fermented food with acidic taste (Younus et al., 2002). In 1907, Dr.Metchnikoff co-workers isolated and named one of the yoghurt bacteria, Lactobacillus bulgaris (Jay,2000). The popularity of yoghurt soared in the 1950 and 1960 with the boom of health food culture. Presently, fermented foods constitute about 25% of the foods consumed worldwide. Usually, these foods are considered safe against food borne infections (Adebayo et al.,2014). The changes in the physical, chemical and microbiological structures of yoghurt determine the storage and shelf life of the product (Sofu and Ekinci, 2007). Fungi, especially the yeasts are a major cause of spoilage of yoghurt as low pH provides a selective environment for their growth. The use of poor quality of milk, unsuitable starter culture, improperly cleaned utensils, and unfavourable temperature of incubation, are responsible to lower the quality of yoghurt (De,1980).Yoghurt should not be freezed, as it affects the texture and quality. Further, it should be protected from other foods with strong odour by sealing it tightly. Yoghurt should be kept in refrigerator after it is purchased. Clean spoon should be used to take yoghurt into the bowel. In order to avoid contamination, it is imperative not to return unused portion of yoghurt to the original container. Yoghurt produced under good manufacturing practice (GMP) should not contain > than 10 yeast cells, and should have a shelf life of 3-4 weeks at 5 0c. Yoghurt having initial yeast counts of >100 CFU/g tend to spoil quickly (El- Bakri et al.,2009). Hygienic practices in the production can improve the microbial quality standards of yoghurt. Strict supervision and stringent quality control standards are imperative to improve the microbial safety of the product, and ultimately reduce the microbial hazards. This communication describes the hygienic and microbiologic quality of yoghurt. Manufacture of Yoghurt Yoghurt is a dairy product prepared by bacterial fermentation of milk. The equal amount of two pure culture of bacteria, namely Streptococcus thermophilus and Lactobacillus bulgaris is added to whole or defatted homogenized milk to make yoghurt (Mahindru,2009).The starter cultures determine the body, texture and flavor of the final yoghurt (Chandan and Kilara,2013).They preserve the food by
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synthesis of lactic acid bacteria, and antimicrobial substance (Hui,2004).Fruits in yoghurt provides aroma, which is very much enjoyed by everybody (Mesurolle et al.,2013). The step by step manufacturing process of yoghurt is mentioned by Lourens-Hattingh and Viljoe,2001). 1. Homogenized whole or low milk fat 2. Addition to skim milk powder 3. Heat treatment at 80 0c to 90 0c for 30-60 minutes 4. Cooling of milk to 40 0c to 45 0c 5. Addition of bacterial culture (2%) at 40 0c to 45 0c 6. Incubation at 43 0c 7. Fermentation stopped by cooling to 4 0c 8. Addition of sugar and fruits 9. Proper packaging 10. Storage at 4 0c Composition and Nutritive value of Yoghurt Yoghurt contain fat (0.0 to 3.5%), solids not fat (8.25-14%), sugar (0-10%) ,and stabilizer (0.0 to 2%).It should be free from any substance foreign to milk such as animal body fat, vegetable fat, and mineral oil. Yoghurt is another name for curd, and in India, it is very popular by the name of ‘Dahi’. About 100 g of edible portion of curd from cow milk contains moisture 89.1%, protein 3.1%, carbohydrate 3.g %; and also calcium 149 mg, potassium 130 mg, phosphorus 93 mg, sodium 32 mg, and iron 0.2 mg (Mahindru, 2009) Yoghurt provides a dietary source of protein, calcium, magnesium, potassium, folic acid, vitamin B6, vitamin B12 and riboflavin. Types of Yoghurt Generally, yoghurt is divided into three categories (De Vuyst and Degeest,1999). 1. Firm yoghurt 2. Stirred yoghurt 3. Drinkable yoghurt Different types of yoghurt are commercially available, which include non-fat yoghurt (99% free), low fat yoghurt and plain yoghurt. Skimmed yoghurt, partly skimmed yoghurt, sweetened yoghurt, fruit yoghurt, and floured yoghurt are also available (Mahindru, 2009). Uses of Yoghurt Yoghurt is liked by everyone including, the children, young, adult, and old throughout the world. It is a rich versatile food capable of enhancing flavour and texture of many cooked and uncooked dishes. It can be used in several ways. 1. Yoghurt is eaten, as it in fresh form. 2. It is used in manufacturing of bakery products. 3. Yoghurt is added to salted or sweetened foods. 4. It is used in preparing the soups. 5. Yoghurt is added in cold and ice drinks. 6. It is mixed in raw vegetable salad. 7. Yoghurt is added to curried chicken. 8. It is added in ice beverages with some water. 9. Yoghurt is used in manufacturing of sauces. 10. It is used as a substitute of fresh cream in cold sauces. 11. Yoghurt is consumed with sugar, honey, jam or dried fruits as a desert. 12. It is added to the egg curry. 13. Yoghurt is taken with potato mixed Chapatti (Paratha) during breakfast in India. 14. It is eaten by mixing in banana with sugar. 15. Yoghurt is mixed with breakfast cereal. 16. Used to prepare ‘Raita’ in India. It is mixed with any of 26
the vegetables such as cucumber/carrot/potato/onion/ tomato etc. Raita is mainly served during lunch. 17. In India, dahi (yoghurt) is frequently used in making ‘Panchamrit’ for offering to God at the time of religious functions. Health Benefits of Yoghurt The main source of probiotic bacteria are fermented dairy products, for example, yoghurt. Probiotic bacteria are beneficial to human health as they improve the gut microbiota balance and defenses against pathogens. The health benefits attributed to probiotics are reviewed by Pal and Jadhav (2013b). Some kind of yoghurts contain probioties, which are tiny organisms, live inside the human digestive system. Yoghurt improves lactose digestion and eliminates the symptoms of lactose intolerance (Guarner et al., 2005). Hence, it provides a nutritional alternative for people with lactose intolerance. It is quickly digested, as more than 90% of yoghurt can be digested within an hour, as opposed to 30% for milk. Yoghurt stimulates immune system, reduces blood cholesterol and high blood pressure, prevents osteoporosis and cardiovascular disease, alleviates the pruritis, canker sores, aphthous ulcers, diarrhoea, bleeding piles and besides possesses antibacterial and ant carcinogenic activities. It is a calcium powerhouse, and a source of high quality protein. Calcium maintains bone density and strength throughout life. Adult person requires 700 mg of calcium per day. As yoghurt is rich in potassium, it helps to keep the blood pressure normal. Hygienic Aspect of Yoghurt Several hygienic steps required for the production of good quality of yoghurt is described (Pal, 2012). 1. Milk of good quality (pasteurized) should be employed in the preparation of yoghurt. 2. Use of raw milk with high microbial load causes a reduction in the quality of yoghurt. 3. As sugar can be the major source of yeasts, moulds and bacterial spores, it is advisable to use the sugar having mesophilic count of less than 20, and yeasts and moulds count less than 1.0 per gram. 4. It is emphasized that fresh and frozen fruits should not contain yeasts. 5. The skim milk powder and chocolate should be of high microbiological quality. 6. The utensils used in the manufacturer of yoghurt should be properly cleaned and washed, as unclean or inadequately washed utensils are responsible for the high total bacterial count. 7. Table, floor and other sites in the dairy plant should be kept in good sanitary condition, as they are a potential source of yeasts and moulds. 8. Flvouring agents should be handled, and stored in cool and dry condition to avoid contamination. 9. Potable soft water should be used in dairy plant as contaminated water can serve as vehicle for spoilage organisms. 10. Dairy plant should be inspected daily, and microbial tests should be carried out periodically by using swab and rinse methods. 11. Aqueous solution of colour made in boiled water is safe to add in the final product. 12. The packaging materials must be effectively sanitized before use, since they act as good source of fungi.
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Proper packaging under hygienic conditions can enhance the shelf life of the product. 13. Good hygienic practice (GHP), and good manufacturing practice (GMP) can reduce the level of microbial contamination. 14. It is imperative that strict hygienic measures must be adapted during the preparation, storage, and distribution of milk products including yoghurt. Microbial Spoilage of Yoghurt The dairy industry manufactures a wide rand of milk products, which are considered perishable. Microbial contamination of dairy products including yoghurt may occur from various sources including utensils, environment, handler, additives, and packaging materials. A large number of microbes, which cause spoilage, are isolated from yoghurt (Pal,2013). 1. Bacteria- Bacillus subtilis, Enterococcus fecalis, Pseudomonas aeruginosa, Proteus , Streptocouccus agalactiae, S. epidermidis 2. Fungi- Alternaria, Aspergillus, Cladosporium, Geotrichum, Kluyeromyces, Mucor,Neurospora, Penicillium, Rhizopus, Saccharomyces The mould and yeasts are the common spoilage organisms of fermented foods (Filtenborg et al.,1996; Robinson,2000).The presence of Aspergillus and Penicillium in yoghurt should be viewed seriously as both the fungi produce mycotoxins, which are deleterious on human health (Pitt and Hocking,1999; Pal, 2002). Microbiological Evaluation of Yoghurt Quality of any food product can be defined against a wide range of criteria such as physical, chemical, microbiological, and can be judged by a range of tests. Microbiological profiling of yoghurt can provide information regarding the hygienic practices adopted during the product making, and subsequent packaging, handling, storage, and distribution (Pal,2013).Food borne diseases and microbial spoilage of food result from the failure or inability to control the microbes at one or more stages of production. The microbiological criteria are essentially of three types. 1. Standards 2. Guidelines 3. Specification Microbiological examination of yoghurt is essential to have a good quality of product, which is safe and wholesome to the consumer. The spoilage of yoghurt can be detected by employing various test such as standard plate count, psychrophilic count, coliform counts, etc. ( Dardashti et al., 2001; Marshall,2001; Karagozlu et al., 2005; El-Malit et al., 2013; Pal, 2013).The total microbial count in food can be determined by pour plate method using standard microbiological techniques. Aerobic colony count is the estimation of viable bacteria based on counting colonies grown in nutrient agar plate.This provides an indication about the sanitary quality of the food. Nutrient agar and malt extract agar are most commonly employed to recover bacteria, and fungi, respectively. Mac Conkey agar is used to determine coliforms. All bacterial and fungal counts are expressed as colony forming units per milliliter or per gram for liquid and solid foods, respectively (Adebayo et al., 2014). The isolation and identification of bacteria and fungi is carried out as per the description given by others (Holt et al.,1994; Pitt and Hocking,1999; Pal,2007a).The occurrence of each isolate 27
in the food sample is determined as a percentage of the total number of food samples, and recorded as the frequency of occurrence (Adebayo et al., 2014). Sabouraud dextrose agar with chloramphenicol and Pal sunflower seed media are used to recover fungi from raw milk (Pal, 2007a).It is advised that the efficacy of both media should be studied for the isolation of moulds and yeasts from yoghurt. Microbiological Specifications of Yoghurt A microbiological criterion defines the limit above, which the food is considered to be contaminated at an unacceptable level with a microbe, its toxin or metabolite, and therefore, considered to be unsafe for human consumption. Undesirable microbes constitute the primary hazard to the safety, quality, and wholesomeness of milk and milk products. In order to maintain the safety of the dairy products, microbiological guidelines is an essential requirement (Pal, 2013). Food Safety and Standards Authority of India established under the Food Safety and Standard Act 2006, is the regulatory body related to food safety and laying down of the standards of food in India . The microbiological criteria of yoghurt/dahi under Indian regulations is presented in Table 1. TABLE 1 : Microbiological Standard of Yoghurt/Dahi Requirement Total plate count Coliforms Anaerobic spore count Escherichia coli Listeria monocytogenes Salmonella Shigella Staphyloccus aureus Source: Pal (2013)
Yoghurt/ Dahi < 10, 00, 000 cfu/g < 1o cfu/g 0 cfu/g 0 cfu/g 0 cfu/g 0 cfu/25g 0 cfu/25g < 100 cfu/g
The microorganisms such as Campylobacter jejuni, Listeria monocytogenes, Salmonella, Staphylococcus aureus, Vibrio cholerae, V.parahaemolyticus and Yersimia enterocolitica are known human pathogens (Pal,2007b), and hence should be absent in all types of foods . CONCLUSION Yoghurt is an excellent milk product due to its nutritional and health benefits. Microbial spoilage of milk products results into a great financial loss to the dairy industry. Strict hygienic practices must be followed during production handling and distribution of yoghurt. The authority should issue the license to small dairy producers after the assurance of minimum level of good manifesting practice. The active role of Government legislative bodies in monitoring the quality of dairy products including yoghurt is greatly emphasized. It is suggested that simple, easy and less expressive techniques should be developed for rapid detection of slow growing psychrotrops and fungi in milk products. This mill help in finding the niche environment in processing units, which lead to post process contamination of dairy products including yoghurt. ACKNOWLEDGEMENT We are highly indebted to Prof.R.K.Narayan for going through our manuscript. Sincere thanks are also due to Miss Tadye Alemu for her excellent typing of the manuscript.
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Use of whey as a substrate for the production of alcoholic beverages has also been exploited. A variety of beer like products has been produced from whey. Interest in these beverages was greatest in Germany during and after the Second World War when sources of fermentable carbohydrates were in shortage .Description of four beers like beverages which have been made from whey are: a) An alcoholic whey beer b) A malted whey beer c) A whey malt beer and, d) A whey nutrient beer. Several research workers have shown keen interest in the production of wine from cheese whey after deprotienization of whey and heating at 820C for 5 minutes approximately 22% dextrose is added depending upon the amount of alcohol desired in wine Fermentation is completed in 7 days at 22-25 0C using the yeast Saccharomyces cerevisiae. As the whey itself contains sufficient nutrients for the growth of yeast, no additional nutrients are added. Preparation of Fermented Whey drinks ‘Acidowhey’ The process of Acido whey making has been developed at NDRI, Karnal. In this process, whey from paneer, cheese, chhana or casein manufacturing is first separated to remove fat and traces curd particles. Clarified whey is heat treated to 85-900C for 10 min. or its equivalent combination. Clarified whey after cooling to 400C is inoculated with an active culture of L. acidophilus and incubated at 39±100C for 20-22 hr. After incubation, fermented whey is clarified to remove precipitated cellular mass, whey protein and minerals formed during the process. Sugar is then added to the product @1012% in the form of 50% sugar syrup which had been earlier pasteurized. At this stage desirable amount of pine apple flavor or any compatible citrus flavor is added. The beverage is now chilled to 400C and packaged. Beverage should be pasteurized before packing or alternatively pasteurized in the container. Additional studies demonstrated antibacterial properties of ‘Acidowhey’ against certain gram positive and gram negative organisms such as Micrococcus flavus, Staphylococcus aureus, Escherichia coli and Bacillus subtilis. LITERATURE CITED 1. Alam, M. T., Singh, Sudhir and Broadway, A. A. 2002. Utilization of paneer whey for the preparation of tomato whey soup. Egyptian J. Dairy Sci. 30: 355 - 361. 2. Beucler, J., Drake, M. and Foegeding, E. A. 2005. Design of beverage from whey permeate. Journal of Food Science 70 (4): 5277-5285 3. Bounous, G., Batist, G. and Gold, P. (1989). Immunoenhancing property of dietary whey proteins in mice: role of glutathione. Clin. Invest. Med. 12: 154 - 161. 4. Geilman, W. G., Schmidt, D., Herfurth-Kennedy, C., Path, J. and Cullor, J. 1992. Production of electrolyte beverage from milk permeate. Journal of Dairy Science, 75: 2364-2369. 5. Holsinger, V .H. Postali, L. P. Devilbliss, D. and Pollansch, M. J. 1973. Fortifying soft drinks with cheese whey protein. Food Technology 27 (2):59-60. 6. Horton, B. S. (1995). Commercial utilization of minor milk components in the health and food industries. J. Dairy Sci. 78: 2584 - 2589. 7. Jagielski, V. 1871. Improvement in dietetic compounds from milk. U. S. Patent 117,889. 8. Jayaprakasha, H.M. and Anathakrishnan, C.P.; Atmaram, K. and Natarajan, A.M. 1986. Preparation of soft drink from clarified and deproteinized whey. Cherion, 15 (1): 16-19. 9. Khamrui, K. 2000. Development of technology for concentrated and dried whey based fruit juice mixes. Ph. D. Thesis, National Dairy Research Institute (Deemed University), Karnal, India. 10. Khamrui, K. and Pal, D. 2003. Effect of storage temperature on microbiological and sensory characteristics of whey based Kinnow juice powder. Indian Journal of Dairy Science, 56 (2) 77-80. 11. Mann, E. J. 1994. Dairy beverages. Dairy Ind. Intl., 59 (11): 16-17. 12. Marshall, K. R. and Harper W. J. (1988). "Whey Protein Concentrates," in Trends in Utilization of Whey and Whey Derivatives, Bull. 233, IDF Brussels, Belgium, 1988, p. 21. 13. Reddy, G. J. Rao, B. V. Reddy, K. S. and Venkayya, D. 1987. Development of a whey beverage Indian J. Dairy Sci., 40: 445-450.
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